


Why Don't You Know My Heart? (I Must Let You Know)

by starryeyed (silentghost)



Category: TWICE (Band)
Genre: Aliens, Alternate Universe - College/University, Childhood Friends, Crack, Crack Treated Seriously, Declarations Of Love, F/F, Friends to Lovers, Hirai Momo is Whipped, Kinda, Not Beta Read, Science Fiction, Telepathy, barely there 2yeon, but not, everyone is ooc soz, it's like the signal mv, surprisingly soft
Language: English
Status: Completed
Published: 2020-06-29
Updated: 2020-07-06
Packaged: 2021-03-04 06:21:55
Rating: Teen And Up Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 2
Words: 3,202
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/24578974
Author URL: https://archiveofourown.org/users/silentghost/pseuds/starryeyed
Summary: It's been a hard first semester for Momo. One day she realizes she's in love with her best friend of fifteen years, the next she's caught up in an alien liberation???--Momo’s been in situations like this before, although not as life threatening, where she would help out Dahyun with whatever goal she had. The summer before she left for college, it was feeding all the stray dogs in their town. Now, it seemed saving a family of aliens would do the trick. Is it simping if she's your best friend who's oblivious to your true feelings?
Relationships: Hirai Momo/Kim Dahyun
Kudos: 14





	1. part one

**Author's Note:**

> so i [built a fanfic in buzfeed](https://www.buzzfeed.com/roldanjudith/create-your-fanfic-and-i-will-tell-you-an-album-to-cnpvhkvjw7) and used it as a prompt for this beauty
> 
> this is my first fic please be nice

Momo was officially done. She had to skip lunch in favor of catching the bus for the five hour trip home, and she was exhausted. Winter break started today, and she already wanted to go back to her college dorm. Laying in bed all day complaining to her roommates Jeongyeon and Jihyo seemed way better than having to deal with-- whatever this shit was.

Dahyun looked a little different, was the first thing she noticed. The last time they saw each other was during Chuseok, back when her hair was an icy blond and not the purple-white gradient it was now. But she looked at home sprawled on Momo's bed in a large checkered sweater, the walls covered in photos and dance trophies from her childhood. What didn't belong was the alien standing in the middle of her room.

"I'm telling you, Momo-unnie, I met this alien in the woods!" Her friend of fifteen years was waving frantically at the short figure before her. They had huge black eyes, a round green head that only just reached Dahyun's waist, and, interestingly enough, a blue three piece suit on. Two antennae stuck out from where ears would normally be on a human, like Shrek but much cuter. 

The alien turned their buggy eyes towards her and lifted their hand. **Hey.**

She scrambled backwards bumping into her suitcase on the way down. Earlier she barely had any time to settle in before her best friend barged into her room, carrying the extraterrestrial like a giant baby. "Dahyun-ah, why are they saying things inside my head?"

Dahyun turned to them, pursing her lips. "Julius Caesar, I didn't know you could talk! I thought we were friends."

**I apologize. Only a select few humans can hear me,** they wrung their hands uncomfortably. 

Momo repeated what they said and Dahyun looked mollified. Momo clambered back to here feet and sat next to Dahyun. She looked between the two. "Okay, can you explain everything that's going on?"

Dahyun recounted a random trip to the forest that surrounds the small town they live in, saying she found the alien wounded and lying on the ground. She brought them back to her house and took care of them for a few days, and by the time they healed completely Momo had arrived at the bus terminal. Momo was _always_ there for her when Dahyun needed help, so the alien accompanied her in welcoming Momo home.

"I've been calling them Julius Caesar V because we're learning about ancient Rome in my history class, and I thought a cool alien deserved a cool name," she finished. "Are you cool with that, alien-ssi?"

**Your language has no sounds for my real name. Julius Caesar is Fine.**

Momo relayed their message once again, and Dahyun clapped her hands, eyes scrunching up into mini crescents.

"Okay, what do we do now? Can we help you get home, Julius?" she asked.

**I must rescue my family. I can only return to my planet with them.** They pointed to a window. **They're somewhere in the forest where you found me.**

Dahyun whipped out her phone and began to type furiously. "Sounds like we're gonna need help with this. Luckily, I know some people who can!"

An hour later, four more girls crowded Momo's room. "This is Tzuyu, Mina, Chaeyoung, and Sana, my friends," Dahyun said. Sana, the girl with long orange hair, waved. Surprisingly, none of them were shocked at the alien's presence. They all sat on the floor on large cushions that Momo's mother brought up.

"Don't be so reluctant, unnie," Dahyun teased, dragging Momo down to the floor so that they all sat in a circle with Julius Caesar in the center and Momo's legs rested in her lap. "You know you're helping me out because you _love_ me."

Momo couldn't deny it. She was right, after all.

You heard her. Kim Dahyun, friend to all-- including extraterrestrial apparently-- was the love of Momo's life. It only took her a semester away from home to realize it.

Oh, if only Jeongyeon could see her now.

Momo's been in situations like this before, although not as life threatening, where she would help out Dahyun with whatever goal she had. The summer before she left for college, it was feeding all the stray dogs in their town. Now, it seemed saving a family of aliens would do the trick. Is it simping if she's your best friend who's oblivious to your true feelings?

Jihyo seemed to think so.

"You need to tell her, Momo. Seeing you mope around is ruining the mood."

It was the week before finals, and Momo obviously wasn't focusing on her English essay that was due in three hours. Her, Jihyo, Jeongyeon, and Jeongyeon's girlfriend Nayeon had their books spread throughout the small dorm. Amidst moaning over past participles and illogical spelling rules, she came to the revelation that she was in love with Dahyun.

Jeongyeon decided the to butt in with, "Yeah, this is just sad."

Momo gasped in betrayal. She was friends with both of her roommates, but Jeongyeon was closest to her. They even bonded over cutting each other's bangs! And now she was calling her out for her unrequited love? Mutiny.

"I _can't_ do anything though!" Momo insisted. "We're best friends, unnie. She basically sees me as a sister."

"That's not what her instagram says," Nayeon said. She shoved her phone with Dahyun's profile pulled up in Momo's face. "Every single post either has you or a caption mentioning you."

Momo whacks her hand away. "She always acts like that! Can we please go back to studying?"

"If you say so," all three of them said in unison. They continued looking at their books, but Momo couldn't focus at all anymore.

_Even if she likes me, that doesn't mean she_ loves _me._

**Momo-chan.** Julius Caesar's mind-voice called her to attention. Momo blinked, looking at the girls around her. **Dahyun was asking you to translate for everyone.**

"Oh, yeah, of course." Momo listened closely and repeated everything the alien told her.

Julius Caesar came from a planet far from Earth's galaxy. Their family worked as miners for the community, digging up precious gems and metals for trade. One day, a portal opened deep in the mines. Curious, Julius approached it and was captured by humans in lab coats along with their family. The humans even took samples of the rocks and soil in the mine.

The lab was unbearable for the aliens. Sterile, white walls, blinding fluorescent lights, concrete floor. It was nothing like the lush mountains of the planet they were used to. For days, the aliens were tortured and made to work for the humans. They filled bottles with pigmented solutions and had to test them on occasion.

Julius Caesar barely escaped with their life. By the time they finished their story, Dahyun's friends were moved to tears.

"You poor thing," Sana sniffled.

Caheyoung got up to hug the alien. "We'll help you."

"Now that we know why you called us here," Tzuyu, the tall girl with dark, wavy hair, chimed in, "let me reintroduce ourselves. At school we're the computer club, but we actually hack into major corporations' databases."

"Eat the rich, unnie," Dahyun said with a grave face. Momo found herself nodding along with the other girls and even Julius Caesar.

Mina, the girl with round cheeks whose hair was pulled into a ponytail, sat up. "Sounds like you were working with makeup, alien-ssi. We should start looking into beauty companies with labs based in Korea. That way we can--"

"--Already ahead of you," said Dahyun and Sana. They had their phones out, numbers flashing across the screens.

"According to my scans, there's an underground lab located right where you found Julius-ssi," Sana said. "I can't figure out what company it is, though."

"Just a sec," Dahyun held up a finger. Everyone leaned closer to her in anticipation. "It's a new research lab for--" she showed the screen to everyone--

"Kylie Cosmetics?"


	2. part two

“That. Was not what I was expecting,” Chaeyoung breathed.

The girls stared at the screen. There was no mistaking it. Julius Caesar the alien was taken by scientists working for Kylie Cosmetics.

Momo withdrew her legs from Dahyun’s lap and abruptly stood up. “Okay, I need food to process this.” She walked to the door. She glanced back into the room and caught Dahyun’s eyes. A question lurked in her best friend’s obsidian orbs, a  _ will you still help me, unnie? _

And Momo, the best friend simp she was, nodded her head  _ yes _ .

She stumbled down the stairs and walked straight to the kitchen, filling a bowl with rice puffs and thinking  _ fuck it _ before grabbing a few packs of dried seaweed and a bag of jelly snacks too. 

This was beyond Momo's scope of experience. Dahyun, an amateur hacker? And, on top of that, a conspiracy involving a major makeup brand?? They were just five high schoolers and a hungry college student-- what could they do? Jeongyeon, save her now.

"Oh, Momo!" Her mother caught her by the elbow and spun her so they faced each other. "Welcome back. You've been so busy with Dahyun I never had a chance to look at you properly."

She hugged her as tight as she could with the bowl between them.

"Sorry about that, Mom…"

"No worries!" She cupped Momo's face, smiling. "My girl's all grown up. Your girlfriend missed you so much when you had to go back after Chuseok, you know. Spend all the time you need with her."

"My-- What? Mom, we're not dating." Momo's grip on the snacks-- and on life, it seemed-- was starting to slip. "Uh, I gotta go."

Momo pushed past her mother and ran upstairs. The short confrontation with her mother rattled her.  _ Dahyun, my girlfriend?  _ she thought.  _ If only. _ She paused just outside her bedroom door, which was opened just enough for Dahyun to be in view. The purple haired girl was talking animatedly to Tzuyu and Julius Caesar. Momo let herself stare in awe at her friend. 

Dahyun  _ glowed _ in the afternoon sun, absolutely in her element as they strategized ways to help the alien and their family get back to their planet. She looked so  _ beautiful _ , even when talking about-- hotwiring cars?

"I thought we were going into the woods?" Momo nudged the door further open and held up the snacks. The girls cheered, and within seconds the bowl was grabbed by Chaeyoung and she was happily munching on the rice puffs.

Sana pouted. Momo had hardly any time to mourn her snack before they got back to business. "Well, yeah, we're just going through our options," the orange haired girl said.

"I said you could carpool everyone to my house, unnie, but we weren't sure if you'd even want to," Dahyun said with a glimmer in her eyes.

Truthfully, the idea made Momo feel a little more helpful. She didn't know anything about planning heists or hacking, but she sure as hell could drive. "I'm down."

"Great!" Dahyun grinned, leaving Momo faint from her brightness. "So here's the plan."

They were going to rescue Julius' family tomorrow night, less for the girls to gather details on Kylie Cosmetics for a future exposé and more to give Momo an opportunity to rest after such an eventful day. At 9 pm, Momo would pick up the other girls and drive to Dahyun's house. Then, they would sneak through a hidden entrance that Sana located in the woods and follow the alien to find their family.

"How exactly are we getting inside?" Mina asked.

Julius Caesar raised their hand at that.  **I can help. We just need to be near the lab,** they said. Momo raised her eyebrows at the vague answer but told everyone the alien had it covered.

Satisfied, Dahyun sat back. "Well, ladies, sounds solid. Now leave so Momo and I can sleep!"

Momo glanced at the window. She didn't even realize their planning took  _ hours _ and the sky was already dark. She turned back to see Dahyun ushering the girls out of her room and patting Julius' head with a smile.

"You're sleeping over?" she asked.

"Your mom invited me for dinner," Dahyun said with a smirk, "and I couldn't say no to spending more time with my favorite unnie~"

Momo laughed. "Yah, I'm your only unnie."

Her smirk deepened. "Even better."

Later, with Julius tucked safely on a spare sleep mat, Dahyun slipped into bed to lay facing Momo. Her eyes were closed, but she knew she wasn't sleeping.

"Momo?" she whispered.

"Yeah, Dahyunnie?"

They finally made eye contact. Dahyun's eyes searched hers in the dark.

"Thank you."

"Of course," Momo replied. _ I would do anything for you, _ she wanted to say.

  
  


-

  
  


Momo, for lack of a better word, was nervous  _ as fuck.  _ She clutched the steering wheel with white knuckles, Dahyun chilling in the passenger seat with Julius Caesar in her lap and the rest of the girls in the back. She was having the time of her life arguing with Sana over some computer program. Mina and Tzuyu were helping conceal each other's hair in dark beanies. Chaeyoung even went as far as dressing in all black with a ski mask pulled over her head.

Momo felt underprepared in her dark sweats and prescriptionless glasses. The whole day was a series of sucker punches to her nerves, first waking up remembering there's an alien in her room and then dealing with her mom spoiling Dahyun during meals. It didn't help that in the morning Jeongyeon called looking for updates on her sad love life.

_ "Just tell her you coward, you have nothing to lose!"  _ Her voice crackled with the poor reception that a small, secluded town entailed.

Momo, knowing she was about to risk her life for the sake of an extraterrestrial family, could only reply, "I'll think about it, Jeong" before hanging up.

Eventually they found their way across town to Dahyun's little house at the edge of the woods. The trek to their destination surely didn’t take long, but to Momo it felt like an eternity. Finally, the group stopped at a clearing.

Trees towered over them in a large circle, the leaves so dense above them that no other plants grew. Pine needles muffled their steps until Sana bade them to stop in front of an old stump.

“My map shows a tunnel leading to the lab here.”

It finally hit Momo. They were really doing it. Julius Caesar walked up to the stump and smacked it. Their palm, laying on the stump, glowed and the ground beneath them rumbled. The soil shifted, and the group fell into the ground.

“Wha--!”

A few seconds of weightlessness, and then a hard impact on concrete. “Is everyone alright?” Tzuyu asked. Stray pine needles stuck out of her hair, with even more lightly raining down from the hole they fell from. Momo helped her back on her feet and looked around. They were at the end of a long corridor, the sparse lights casting shadows on every corner.

"We're here!" Dahyun grabbed Momo's wrist. "Let's get it."

The laboratory was still new and apparently had minimal security. The two led the group down the hall, stopping at a heavy metal door. Momo turned the knob, and they entered a lab with all the lights turned off. The girls shined their phone lights on tables full of empty tubes and weighing scales. Chaeyoung pointed the light toward a corner, where a group of huddled figures sat.

Julius rushed forward and dropped to their knees, shoulders shaking. The other aliens' eyes widened in disbelief. They were dressed in suits similar to Julius', albeit dirty and torn.

"Is this your family?" Dahyun tugged Momo forward and the girls followed.

They nodded.  **Yes. Thank you, Dahyun. Thank you.**

She didn't need Momo's interpretation to understand. The two hugged. Mina said in a hushed voice, "We're here to rescue you. If you show us how to open the portal you came through we can help you home."

The shortest alien nodded vigorously and moved as if to show her. Then they froze.

A gun cocked. They whipped their heads around, eyes widening as Kylie Jenner herself walked into view. “Rise and shine bitches~~,” she sang off-key in heavily accented Korean. “What the hell are you doing in my lab?”

"This wasn't in the plan." Momo was starting to panic. She pushed Dahyun behind her. Kylie waved the gun.

"Hands up, all of you. I can't have this secret of mine coming out and ruining my reputation."

She pointed the gun at Momo first. They were doomed. They were trapped in this lab, underground and unknown to the public, and they were going to die at the hand of a millionaire, and she never even got to tell Dahyun she loved her--

"Hey, what the--!"

Suddenly Julius' arms were raised, and with a flick of their wrist the gun flew out of Kylie's hand and into the wall. She cried out as unseen forces pushed her against the ceiling. The other aliens raised their arms as well, keeping her suspended.

The short one tugged on Momo's arm. They led her and the girls to a side room, where a platform and a control table sat. A simple red button with the label OPEN/CLOSE blinked at them. 

"That simple, huh?" Momo pushed the button and a glowing purple portal opened up on the platform. "Go get your family. Let's bring you home."

One by one the aliens entered the room with Julius taking up the rear. Surrounded by their family, they looked at Momo.  **We locked her in a broom closet. With our combined powers, we'll destroy the portal and any information on it so they can never find us again. Thank you, Momo-chan.**

They waved inside the portal as they transported to their home planet. The platform collapsed on itself, and the portal was gone. 

The girls made their way above ground through a hidden stairwell near the hole they fell down. They emerged from the old stump, squinting at the bright moonlight. The stars were out. The other girls chattered about what had just happened as they walked in the direction to Dahyun’s house. Momo and Dahyun hung back a few feet behind them, still holding hands.

"I heard you back at the lab," Dahyun said. "Before we sent the aliens off."

And Momo.exe has stopped working. She knew what Dahyun was talking about. Oh God. Momo actually said that part about confessing out loud. Oh shit. Oh fuck.

She laughed, "Oh, my silly peach unnie," and then--

They kissed. And it was almost like every single kiss Momo’s had in her life but ten times better because it’s  _ Dahyun _ , and Dahyun was  _ kissing  _ her.

Dahyun pulled away with another laugh. “Let’s have a sleepover again, Momo!” she said before skipping ahead to join her friends. Momo was left smiling harder than she could imagine. She pulled out her phone and dialed the only person who would pick up at such a late hour.

“Hey Jeongyeon, you’ll  _ never _ guess what I just did.”

**Notes for the Chapter:**

> i blacked out and this just appeared on my computer //j  
> don't let your memes be dreams yall

**Author's Note:**

> me holding this ship up: i jus think elsa dahyun is neat
> 
> disclaimer: from my knowledge kylie cosmetics is animal cruelty free! this brand has other issues like lacking diversity in employees and abusive work conditions but extraterrestrials is not! this is fiction! here's a [twt thread](https://twitter.com/methydactor/status/1274827811065417729?s=20) of better makeup brands to support!


End file.
